Harry Potter fans will get the chance to appear in the franchise's next film, thanks to a deal between producers Warner Brothers and Microsoft UK.

Fans will have to complete an online quiz on Harry Potter and the Order of the Phoenix as part of the competition, arranged by Warner Home Video and Microsoft Digital Advertising Solutions' UK division.

Those who answer all the questions correctly will get the chance to appear in the next film, Harry Potter and the Half-Blood Prince.

Warner Home Video UK, which is launching the competition as part of a promotion for the DVD of Harry Potter and the Order of the Phoenix, won an international competition among Warner divisions for the right to offer the walk-on part in the UK.

Josh Berger, the president and managing director of Warner Brothers UK, said his division's victory marked a sea change in the way new media is perceived as a marketing tool.

"It is an indication of how important digital has become in the marketing mix. The level of engagement online is huge," he said.

In turn, Warner held competitive pitches from UK media owners - both digital and traditional - before settling on MSN UK as the right partner for the competition.

"Of all the choices they could have made it is great that a digital media owner was picked to run this competition," said Chris Ward, the commercial director of Microsoft Digital Advertising Solutions.

"This is a big campaign and we can provide that extra level of engagement in the digital space."

The competition, which launches today, will run across the MSN Network in the UK until December 20.

MSN is supporting the competition with a wide-ranging campaign that will include "substantial" editorial space and ad placements across the MSN network – many of which the company says have not been offered to brands before for campaigns.

MSN has also created dedicated Harry Potter "hub" – a microsite accessible via MSN.co.uk – that will be the home for information, clips and trailers.

"Brands and agencies are being forced to change their advertising strategies to engage with consumers and create a dialogue, rather than simply push messages to them," added Ward.

"This deal proves that digital has come of age and is now seen as a mainstream platform to communicate with consumers."

· To contact the MediaGuardian newsdesk email editor@mediaguardian.co.uk or phone 020 7239 9857. For all other inquiries please call the main Guardian switchboard on 020 7278 2332.

· If you are writing a comment for publication, please mark clearly "for publication".